Work got under way in 2012 but it quickly became apparent the extent of what needed to be done was far greater than previously thought.

Water was literally pouring in at some points, the foundations beneath the paving stones were rotten and there was a lot more asbestos throughout the structure than had been identified initially.

What was originally intended to be a limited refurbishment of some parts of the tunnel turned into a wholesale intervention to save it.

So how was the scale of what needed to be done not anticipated earlier?

Outside the Tyne pedestrian and cycle tunnel in Wallsend

Mr Turnbull said: “A lot of it has to do with the limitations placed on developers in terms of investigating listed properties.

“It’s not like you can just go in and start smashing things and pulling things up.

“We’ve asked ourselves, ‘how did we not see this coming?’ but we did all the assessments we were able to and we were shocked when the full scale of the problem emerged.”

The tunnel’s listed status has made other delays inevitable.

Restoration works of the Tyne pedestrian and cycle tunnel in Wallsend

Every last step needs to be approved by heritage managers and skilled conservationists are required to delicately work on the original tiling.

They’ve gone to incredible lengths to replicate any original material which needs to be replaced, including receiving special approval to import a type of coating for the ceilings of the entrance halls from the US which isn’t available in the UK because it was the only product out there which was near-identical to the original.

Mr Turnbull said: “The cruel irony is that, apart from the glass lifts, a measure of its success is that you won’t really be able to notice much difference from the original when you go in, despite how long it has taken.”

In the mean time, the budget began to creep up and the reopening date started to slip further away.

Inside the Tyne pedestrian and cycle tunnel in Wallsend

Then a new problem emerged: towards the end of 2014 it became clear that all was not well with GB Building Solutions and sub-contractors weren’t being paid.

Despite assurances to NECA the firm was just going through a minor blip, the company went into administration in March 2015.

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The £4m of public money it was given? Mr Swan admits it would cost so much to take the company to court to recover the funds it wouldn’t be worth it.

At this point some consideration was given to abandoning the project altogether but regional leaders decided to press on.

Rather than go back out to the market, NECA took the works in-house and immediately secured the site to stop out of pocket sub-contractors reimbursing themselves with whatever equipment they could find lying around.

The budget was increased to £8.63m and a new reopening date was confidently announced - summer 2015.

Restoration works of the Tyne pedestrian and cycle tunnel in Wallsend, steel foundations for the vernacular

But there was a new problem. In the gap between the collapse of the main contractor and resumption of works, the tunnel became contaminated by asbestos fibres from parts of the tunnel’s interior that were left exposed when workers downed tools.

Mr Swan said: “They started the job but didn’t finish it.

“I’ll give them the benefit of the doubt and say I’m sure they’d have cleaned the fibres properly if they’d been able to continue but it didn’t happen and it was contaminated throughout.”

The contamination was so bad only a handful of specially-trained workers with breathing apparatus could enter the tunnel and NECA was forced to tender for a special firm to come in and forensically clean it before work could go on.

Restoration works of the Tyne pedestrian and cycle tunnel in Wallsend, Site manager Robbie Richardson and project manager Stuart Turnbull

“It was just a team of 24 people literally cleaning every inch of the tunnel with tiny brushes and specialist vacuum cleaners for a whole six months”, Mr Turnbull said.

Despite very little happening for two years, the decontamination - plus various fees, rental charges and the cost of running the replacement shuttle bus - cost over £2m during that period.

By early 2017, the budget was up to £12m and work was beginning again after two years - but the curse was intact.

A steel contractor brought in to work on structural improvements recently had to be dismissed, further slowing matters down.

And in the last week or so, things have got even worse.

Vaughan Engineering Ltd, brought in to work on the tunnel’s electrics, announced it is in financial trouble due to the collapse of Carillion.

Restoration works of the Tyne pedestrian and cycle tunnel in Wallsend, steel foundations for the vernacular (Image: ncjMedia)

The firm was owed more than £600,000 by the failed construction giant and had budgeted for a further £1.1m worth of work this quarter alone.

It’s unclear at this stage if Vaughan will survive but Mr Swan and Mr Turnbull admit that, should it fold, it could mean the reopening date needs to be pushed back again to early 2019.

Factor in the 25% inflation in construction costs since 2008, when the sector was still in a post-financial crisis slump, and the years of extra administrative costs, and the total budget is now at an estimated £15,657,198.

It’s a startling jump from the £6m originally forecast a decade ago so the obvious question is this: is it really worth it?

Mr Turnbull said: “We’ve had a lot of bad luck. This has without a doubt been the most challenging project I’ve ever worked on.

The old wooden escalator system

“But it will be worth it - if we decided to scrap it and build another crossing over the Tyne it would costs tens of millions of pounds, even hundreds of millions.

“From our point of view it’s a heritage asset that we are obligated to look after.”

Mr Swan said: “The price has gone up but so has the scope of work and that means we’ve secured this important route over the Tyne for another 60 years.

“Despite the fact that it was built half way through the last century, it’s a completely sustainable and futureproof way to travel - if we want to encourage people to get out of their cars and start using green modes of transport, this tunnel is perfect.”

The end is in sight for a project which at one point looked doomed - but even the last few weeks have provided a reminder that the light at the end of the tunnel can fade.